Burner ignition and fuel control system



Jan. 3, 1956 A. W. LINDBERG ETAL BURNER IGNITION AND FUEL CONTROL SYSTEM Filed Oct. 8, 195] MQ UU United States PatentO 2,729,281 7 BURNER IGNITION AND FUEL CONTROL SYSTEM Allan W. Lindberg, Webster Groves, and James C. Rombach, Rock Hill, Mo., assignors to Missouri Automatic Control Corporation, St. Louis, Mo., a corporation of Missouri Application October 8, 1951, Serial No. 250,375 ,1 Claim. (Cl. 158-28) veloped sufficient speed to assure proper atomization of the liquid fuel. a

In the operation of conventional spray-type oil burners, liquid fuel is delivered at relatively low pressure to an atomizing nozzle which is supplied compressed air by a rotary blower. When the controlling element in the burner control circuit calls for burner operation, the fuel supply means and blower are usually energized simultaneously, and because it requires an interval for the blower to attain suflicient speed to supply pressure for suitable atomization, some undivided slugs of liquid fuel issue from the nozzle during this initial period. This undivided fuel is either unburned or incompletely burned, which, in either case, results in deposits on the nozzle and ignitor which are deleterious to their operation. This problem has been recognized and means have been proposed to delay the flow of liquid fuel until full atomizing pressure is reached.

In the present invention, it is an object to provide a burner control system having a novel fuel ignition device in the energizing circuit of the liquid fuel supply means, which ignition device functions inherently to provide a short delay in the operation of the liquid fuel supply means when the control system calls for burner operation.

A further object of the present invention is to provide a burner control system having a high frequency spark ignition circuit including a transformer, an electron discharge tube supplying energy pulses to the transformer at high frequency, and an electrically operated fuel supply means in the plate-to-cathode circuit of said tube, whereby operation of both the igniter device and the fuel supply means is dependent upon conduction through said discharge tube.

A further object is to provide a burner control system in which a single temperature responsive switch operates to start and stop operation of an electrically operated fuel supply means, electrically operated means for supplying combustion air, and a high frequency electronic igniter tube, which discharge tube is series connected in circuit with said fuel supply means so that when said temperature responsive switch moves to a starting position, the operation of the fuel supply means and the igniter device will be delayed for the interval required to heat the tube cathode, thereby permitting the air supply device to attain full capacity output before fuel is supplied.

These and further objects and advantages will appear upon reading the following complete description in con nection with the accompanying drawing.

In the drawing:

The single figure is a diagrammatic illustration of one form of the present invention.

With reference to the figure, a burner nozzle is generally indicated at 10 which receives liquid fuel through a conduit 11 controlled by an electromagnetically operated valve generally indicated at 12, and which receives compressed air supplied by an electrically operated blower 13 through a conduit 14. The fuel issuing from nozzle 10 in an atomized spray is ignited by an arc bridging the electrodes 15 and 16 of the ignitor circuit.

The burner control system comprises a low voltage circuit including a space thermostat 17 and a relay 18. The circuit is energized through a step-down transformer 19 connected across commercial power supply leads 20 and 21. The source of power is indicated as being that which is most commonly available, volts, alternating current. Further included in this low voltage circuit is a transformer 22 through which the voltage of the power supply is further stepped down to provide a suitable source of and a spark gap illustrated by spaced electrodes 15 and 16. The electron tube is preferably a pentode having a plate 27, a suppressor grid 28, a screen grid 29, a control winding 32, a secondary winding 32a, and the feedback winding 26.

..Power to the ignitor circuit and to the electromagnetic valve 12 as supplied through lines 20-21 is preferably half-wave, rectified by the provision of a selenium rectifier 33 in the supply line 21 and filtered by the provision of a condenser 34 across the supply lines 20 and 21. Plate connected to the cathode 31. The screen grid 29 is connected to the plate circuit at 39, ahead of the transformera resistor 42, and a lead 43, the other side of winding 26 being connected to the cathode by a lead 43a. The cathode 31 is connected to the power supply line 20 through in sa ftsien .qqntluqtien through tube 2. to the .oneratiqn of electromagnetic valve 12 provides the necessary delay in delivery of fuel to the nozzle to permit the blower 13 .to :build up and deliver air at .sufiicient pressure to burner nozzle -10 for proper atomization of ,the liquid fuel. It is to be understood that fuel valve 12 is nor mally closed so as to completely out ofi fuel supply to nozzle 10 and that it opens upon energization of the electromagnetic coil 35.

The power supply to the ignitor circuit being also completed upon closure of relay 18, the ignitor will also begin to function as soon as the cathode is sufiicieutly heated. The operation of the ignitor circuit is basically that .of a relaxation oscillator in which the feedback coil 26 interacts cumulatively with the increase in tube .conductivity or plate current, due to its inductive relationship with primary coil 32, to impose an increasingly strong positive signal on the control grid 39 until discharge saturation of the tube is reached, whereupon the positive grid signal vdrops to zero, effecting a rapid drop in tube discharge. This drop in tube discharge, in turn, reverses the signal on the control grid, and again by cumulative interaction, the tube is rapidly driven to cut-oft. The capacitance of the circuit is held to a minimum so that there is no appreciable capacitive reactance to .continue the fiow of current through the transformer at cut-off.

Current is thus caused to flow intermittently through the primary 32 of transformer 24, with abrupt cut-ofis and at relatively high frequency, which results in high self-induced potentials in winding 32 and mutually induced high potentials in secondary winding 32a. Windings 32a being series connected across the air gap at spaced electrodes 15 and 16, the total potentials built up in these coils is impressed across the gap, resulting in a high frequency arcing suitable for ignition of the atomized fuel. Each time the energy in coils 32 and 32a is dissipated bythe arc, the circuit relaxes and repeats the cycle. The operation of the ignitor circuit illustrated herein is more fully described in our co pending application entitled Electronic Spark Generator, Serial No. 249,852, tiled October 5, 1951, now Patent No. 2,688,108, granted August 31, 1954.

In the control system described above, the ignitor will operate constantly as long as the space thermostat 17 is closed. If, however, it is desirable to stop operation of the ignitor after the burner 10 has been successfully ignited, this may be accomplished by providing the combustion responsive switch 48 and leads 49, 50, and 51,

al show .11 1192129 that when th switsh 4.8 r sponds to the condition of combustion to swing to the left of the position shown, dead 36 will be connected to lead 44 via lead 51, switch 48, and lead and the igniter circuit will thus be shunted.

The foregoing description :and accompanying drawing are intended .to be illustrative and not limiting, the scope of the invention being set forth in the appended claim.

I cl im In aburner controlsystem for pressure type oil burners, a source of electrical power, electrically operated fuel supply means, an electrically operated blower for supplying air for atomization-of the fuel, and a high frequency ignition spark generating system including an electron discharge tube which -wheri conducting provides ignition spark and effects energization of said fuel supply means, said tube including an indirectly heated cathode, a cathode heater, a .control grid and a plate, said spark generating system further including a plate to cathode circuit for connecting said tube across said source of power, which circuit includes in the plate side thereof an ignition transformer primary winding and said fuel supply means, means forming an inductive feed-back from said transformer winding to said tube control grid to effect oscillation, a pair of spaced spark electrodes, an ignition transformer secondary winding and means connecting said electrodes'across said secondary winding, and means including a temperature responsive switch for simultaneously-connecting anddisconnecting said blower, said plate to cathode circuit, and said cathode heater with said sourceof .power, rwhereby operation of the blower and cathode heater is instantaneous upon closure of said temperature responsive switch but operation of the fuel supply means is delayed until said tube cathode is heated to the point of emission.

References (lited ,in the file of this patent UNITED STATES PATENTS 

